Field of the Disclosure
The present disclosure relates to a dry type toner for use in an electrophotographic system.
Description of the Related Art
In recent years, in connection with an increase in a demand for energy saving in image formation, measures for further lowering the fixing temperature of toner have been increasingly taken. As one of the measures, it has been proposed to further lower the fixing temperature by the use of a polyester resin having a low softening temperature. However, since the softening temperature is low, melt-adhesion of toner particles occur in a stationary state during storage, transportation, and the like to cause blocking in some cases.
Japanese Patent Publication Nos. 56-13943 and 62-39428 and Japanese Patent Laid-Open No. 4-120554 have proposed techniques of using a crystalline polyester resin having a sharp melt property in which the viscosity sharply decreases when the temperature exceeds the melting point as a means for achieving both blocking characteristics and low-temperature fixability.
Moreover, Japanese Patent Laid-Open Nos. 2011-107261, 11-202555, 8-184986, 4-21860, 3-150576, 59-18954, and 58-95750 also have proposed toner containing an ester containing ethylene copolymer, such as an ethylene-vinyl acetate copolymer, an ethylene-ethyl acrylate copolymer, or an ethylene-methyl methacrylate copolymer, in order to improve fixability.
When a former crystalline polyester resin has been used as a main binding resin of an electrophotographic toner, the crystalline polyester resin has been excellent from the viewpoint of achieving both fixability and blocking characteristics due to the sharp melt property of the resin. However, the crystalline polyester resin has low electrical resistance, and thus has had a problem with chargeability.
Then, it has also been proposed to use a crystalline polyester resin and an amorphous polyester resin in combination. However, it has been necessary to increase the glass transition temperature of the amorphous polyester resin forming a matrix to be equal to or higher than the storage environmental temperature in order to satisfy blocking property. In that case, it has been difficult to satisfy low-temperature fixability under high-speed printing conditions.
Moreover, Japanese Patent Laid-Open Nos. 2011-107261, 11-202555, 8-184986, and 4-21860 have also proposed to partially blend an ethylene-vinyl acetate copolymer or an ethylene-ethyl acrylate copolymer in toner but it has been difficult to satisfy the low-temperature fixability under high-speed printing conditions only by partially blending the copolymers.
The present inventors have examined, and then have found that it is the most effective to lower the glass transition temperature of a binding resin which is a main component of toner in order to improve the low-temperature fixability at a high speed.
However, it has been disadvantageous to lower the glass transition temperature of a binding resin in that the storage property and the electrical resistance are reduced, so that the chargeability as toner deteriorates. Then, the present inventors have focused on an olefin-based copolymer having high electrical resistance and a glass transition temperature equal to or lower than room temperature. Specifically, the present inventors have attempted to achieve both chargeability and fixability by using, as the main resin, ethylene-acetate ester copolymers such as an ethylene-vinyl acetate copolymer, ethylene-acrylic acid ester copolymers such as an ethylene-methyl acrylate, ethylene-methacrylate ester copolymers such as an ethylene-methyl methacrylate, or the like. However, for the use of a low molecular weight olefin-based copolymer as the main resin of toner as in Japanese Patent Laid-Open No. 59-18954, the strength as resin is low, which has posed a problem with storage stability. On the other hand, for the use of a high molecular weight olefin-based copolymer as the main resin as in Japanese Patent Laid-Open No. 58-95750, the gloss of an obtained image decreases because the melt viscosity in fixing is excessively high. Furthermore, when a high molecular weight olefin-based copolymer is used as the main resin, the dispersibility of a pigment is poor, which has posed a problem that the image density of a fixed substance decreases. Then, the present disclosure provides toner excellent in image quality and excellent in low-temperature fixability in high-speed printing, blocking, and chargeability.